1. Field of the Invention
The present invention relates to a lithographic method that forms ultra-fine groove-form patterns in samples of electrical functional films, optical functional films, resist films, mask-forming films, and the like and more particularly to lithographic method using an ultra-fine probe needle capable of ultra-fine working, which uses an AFM cantilever, nanotube, etc., with a nano-size tip end diameter as a probe needle and forms groove-form patterns with an extremely small groove width in samples.
2. Prior Art
Generally, a lithographic method utilizing a photoresist and a mask (also called an exposure image-drawing method) is used in order to form circuit patterns on semiconductor chips. In this lithographic method, as shown in FIG. 16, a wafer is cut from a single crystal in steps (a) and (b). This wafer is used as a substrate 100, and in step (c) a photoresist is dropped onto this substrate 100 while the substrate is rotated on a spinner, thus forming a photoresist film 102 on the surface of a substrate 100 in step (d).
A mask 104 corresponding to a photographic negative is superimposed on the surface of this photoresist film 102 in step (e), and the photoresist film 102 is exposed from above. The mask 104 is formed by patterning opaque parts 108 in a substrate film 106. These opaque parts 108 prevent the photoresist film 102 from sensing light. When developed, the exposed parts 110 are removed in step (f), while the unexposed parts 112 remain. Conversely, there may be cases in which the unexposed parts are removed. Next, a diffusion layer 114 is formed in the exposed parts 110 by means of a diffusion treatment in step (g), and the unexposed parts 112 are removed in step (h), so that the semiconductor chip 116 is completed. Complex semiconductor patterns are formed by repeating these steps.
Since light is utilized in such an exposure system, the light that passes through the mask is diffracted in the areas of the opaque parts, thus lowering the resolution of the pattern. As the pattern of the mask becomes finer, this diffraction is increased, so that the resolution drops even more abruptly. Techniques in which the exposure wavelength is shortened have been developed in order to increase the resolution. First, development moved from the near ultraviolet of ultra-high-pressure mercury lamps to the far ultraviolet of excimer lasers. However, even in the case of promising excimer laser exposure, the resolution is only about 300 to 400 nm. In semiconductors, there is a demand for further increases in density and speed, and ultra-fine working in the range of 1 nm to 100 nm is impossible using conventional methods.
Accordingly, X-ray exposure techniques utilizing X-rays with a wavelength of approximately 0.1 nm have come to the fore. Although there are no problems in terms of obtaining a high resolution, lenses cannot be used for the directional control of X-rays, and reflection control by means of concave surfaces or convex surfaces is also difficult. Furthermore, there are also problems in terms of the parallel orientation of X-rays. In cases where an ordinary electron beam excitation mode is used as an X-ray source, the intensity of the X-rays is weak. On the other hand, in the case of a plasma X-ray source or SOR light source, the scale of the apparatus is large, so that adaptation for practical use is difficult.
Electron beam exposure has been developed in order to solve such difficulties. Since electron beams have a short wavelength, the resolution is extremely high, and such systems have good operability, as in the case of electron microscopes. On the other hand, however, such systems are inconvenient in that the exposure treatment must be performed in a vacuum. Electron beams also suffer from a drawback in that such beams are scattered in a photoresist, so that the electron beam itself spreads. Furthermore, in the case of electron beams, the energy of the electrons is high; accordingly, such a technique also suffers from the drawback of creating defects in the semiconductor that is worked.
Accordingly, the object of the present invention is to provide a lithographic technique with a high resolution that is completely separate from the concept of conventional exposure treatments using electromagnetic waves or electron beams and makes it possible to draw ultra-fine groove patterns with a groove width of several nanometers to several hundred nanometers on samples such as high-function films, resist films and mask-forming films, etc.
The above object is accomplished by unique steps of the present invention for a lithographic method that forms groove-form patterns on a sample surface (or on a surface of an object), and the unique steps of the present invention comprises the steps of:
causing a tip end of a probe needle to contact a surface of a sample (or an object) either continuously or intermittently, the probe needle being an ultra-fine probe needle with a nano-size tip end diameter,
applying a voltage across the probe needle and sample, and
causing the probe needle to move while removing a substance that makes the sample at a probe needle contact area by an application of said voltage.
In this method, the ultra-fine probe needle is a nanotube probe; and this nanotube probe is obtained by fastening a base end portion of a nanotube to a holder with a tip end portion of the nanotube being caused to protrude from the holder.
In this nanotube probe, the holder is a pyramid portion of a cantilever for AFM use. The pyramid portion is a portion protruding from the cantilever and the shape of the pyramid is free and contains all desired protruding shapes.
Also, the sample or an object on which the groove-form patterns are made is a lithographable matter such as an organic film, other organic matter and an inorganic matter, and a voltage is applied across the probe needle and this organic film so that the probe needle is used as a cathode.
In the method of the present invention, the groove width and groove depth of the groove-form pattern are controlled by adjusting the scanning speed of the probe needle and the applied voltage.
Furthermore, the organic film can be an electrical or optical functional film, a mask-forming film, or a resist film formed on a substrate. Also, the organic film can be a polysilane film.